1. Field of the Invention
The present invention relates generally to a cable system for raising and lowering one or more door panels of an industrial furnace to at least partially open and close a furnace opening that is defined where an access passage opens through a substantially vertically extending furnace face, for example in a steel reheat furnace or the like, with door support cables being wound onto specially configured tracks of shaft-carried sheaves or the like to introduce horizontal components of movement during door raising and door lowering. In one embodiment, a cable system for raising and lowering furnace doors introduces horizontal components of movement as one or more furnace doors are opened and closed to effect door movement away from the furnace face during raising, and door movement toward and into seated engagement with the furnace face during lowering. In embodiments where a plurality of doors are arranged end-to-end to cooperatively close an elongate furnace opening, horizontal components of movement preferably are introduced during door raising to separate adjacent ends of adjacent pairs of the doors, and during door lowering to bring the adjacent door ends toward and into engagement with each other so the doors will cooperate properly to close the furnace opening.
2. Prior Art
Large industrial furnaces such as steel reheat furnaces and the like utilize large furnace door panels to open and close large furnace openings through which large objects such as steel billets must pass when moving into and out of furnace chambers. Reheat furnace openings as tall as six to eight feet and/or as wide as sixteen to eighteen feet are not unusual. To withstand lengthy exposures to the energy emanating from high heat furnace environments, furnace door panels typically are provided with an inner face formed from solid refractory elements, with small spaces therebetween typically being filled with refractory cement, and with added layers of insulation being provided between and behind the refractory elements. To rigidly support the solid refractory materials and accompanying insulation, heavy, perimetrically extending steel frames are employed that support grid-like arrays of interconnected steel components. The resulting door panel assemblies are quite heavy, often weighing between about 4000 and about 8000 pounds.
Known cable systems for raising and lowering industrial furnace door panels doors typically raise and lower the door panels along vertically extending, substantially linear paths of travel. Stated in another way, the door panels are not deliberately caused to execute horizontal movements while being opened and closed, and hence the raising and lowering movements of each door panel tend to take place substantially within a single vertically extending plane, with door movements including no intentionally provided horizontal components of movement.
In industrial environments such as those presented by steel mills, it is important that the cable systems that are used to open and close heavy furnace doors of high heat furnaces be of rugged yet simple construction to minimize the possibility of breakdown and the need for maintenance, and so that, in the event that a problem with a broken cable or other component is encountered, it can be easily diagnosed and quickly corrected. To the extent that present day cable-operated furnace door positioning systems exhibit a degree of complexity, this is usually limited to the addition thereto of such cable reaches and pulleys as may be needed to connect the door panels to movable counterweights that are provided so that door panel movement can be accomplished through the application of external forces of relatively small magnitudes.
Because increases in complexity often bring with them increased risks of failure and resulting "down time," and because component failures in the environment of a steel mill can present very real safety concerns, it is understandable that knowledgeable and experienced personnel often tend to resist the implementation of changes that introduce "complexities. " It is equally understandable that, in in the interests of "keeping systems simple," some operating problems tend to be viewed as "tolerable." One tolerated problem has been damage and wear due to rubbing, bumping and occasional impacts of a raised door panel against furnace face components. As a present-day cable-supported door panel is raised, it tends to rub against adjacent furnace face components causing wear and a need for maintenance and replacement of worn components. Bumping and more severe impacts between the door panel and the furnace face may cause even greater damage and attendant "down time" for maintenance and replacement of broken components. Door service life can be dramatically shortened if brittle solid refractory components are damaged or broken due to impact.
Another tolerated problem has been damage and wear due to bumping and impact of adjacent ends of left and right door panels in installations where door panels arranged end-to-end are used to cooperatively close relatively wide or elongate furnace openings. When adjacent door panels are closed, their adjacent ends should engage to properly close the furnace opening. However, when one or both of the door panels are raised to at least partially open the furnace opening, the adjacent ends of adjacent door panels may move relative to each other while in engagement, thereby causing wear, or may impact and damage each other if one or both of the raised, cable-supported door panels is struck or otherwise caused to swing on its cables.
Unfulfilled by the prior art is a long-standing need for a simple and reliable cable system that is well suited for use in an industrial environment such as that of a steel mill that will minimize engagement, bumping and impact problems of raised furnace door panels in an effort to eliminate wear, breakage, safety concerns and attendant "down time" due to unwanted engagements with cable supported furnace door panels during raising and lowering movements, and while the door panels are supported by cables while in open positions.